What is the recommended dose of cephalexin (cephalosporin) for an adult patient with pharyngitis who is allergic to amoxicillin (amoxicillin)?

Cephalexin Dosing for Adult Pharyngitis with Amoxicillin Allergy

For an adult with pharyngitis and amoxicillin allergy (assuming non-anaphylactic allergy), cephalexin 500 mg orally every 12 hours for 10 days is the recommended regimen. 1, 2

Critical Allergy Assessment First

Before prescribing cephalexin, you must determine the type of penicillin/amoxicillin allergy:

• Non-immediate (non-anaphylactic) reactions (e.g., rash occurring hours to days after exposure): First-generation cephalosporins like cephalexin are safe and preferred 1
• Immediate/anaphylactic reactions (e.g., hives, angioedema, bronchospasm within 1 hour): Avoid ALL cephalosporins due to up to 10% cross-reactivity risk 1, 3

Specific Dosing Regimen

For streptococcal pharyngitis in adults:

• Cephalexin 500 mg orally every 12 hours (twice daily) for 10 days 2
• Alternative: 250 mg every 6 hours (four times daily) for 10 days, though twice-daily dosing improves adherence 2, 4
• The FDA label specifically states that 500 mg every 12 hours is appropriate for streptococcal pharyngitis 2

Why This Regimen

• Strong, high-quality evidence supports first-generation cephalosporins as the preferred alternative for penicillin-allergic patients without immediate hypersensitivity 1, 3
• Cephalexin has narrow spectrum, proven efficacy, and low cost compared to broader-spectrum alternatives 1, 3
• The full 10-day course is essential to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 1, 3

Alternative Options if Cephalexin Cannot Be Used

If the patient has immediate/anaphylactic amoxicillin allergy, use instead:

• Clindamycin 300 mg orally three times daily for 10 days (preferred; ~1% resistance rate in US) 1, 3
• Azithromycin 500 mg orally once daily for 5 days (acceptable; but 5-8% macrolide resistance in US) 1, 3
• Clarithromycin 250 mg orally twice daily for 10 days (acceptable; similar resistance concerns as azithromycin) 1, 3

Common Pitfalls to Avoid

• Do not shorten the course below 10 days (except azithromycin's 5-day regimen) even if symptoms resolve—this increases treatment failure and rheumatic fever risk 1, 3
• Do not use cephalosporins if the patient had anaphylaxis, angioedema, or immediate urticaria to amoxicillin—the cross-reactivity risk is too high 1, 3
• Do not prescribe broad-spectrum cephalosporins (cefdinir, cefpodoxime) when narrow-spectrum cephalexin is appropriate—this unnecessarily increases cost and resistance 3
• Do not assume all "penicillin allergies" are true immediate reactions—most patients labeled as penicillin-allergic can safely receive cephalosporins 3

Adjunctive Therapy

• NSAIDs (ibuprofen) are more effective than acetaminophen for pain and fever control 5, 3
• Avoid aspirin in children due to Reye syndrome risk 3
• Do not use corticosteroids routinely—they provide minimal benefit 3, 5